Preparation method of high-pressure crushable aluminum alloy energy-absorbing box section for automobile

Abstract

This invention discloses a method for preparing high-pressure crush-resistant aluminum alloy energy-absorbing box profiles for automobiles, relating to the field of aluminum alloy material processing technology. The method includes alloy composition ratio and casting, two-stage homogenization treatment, design of a special extrusion die, precision extrusion, high-strength online water quenching, and controllable aging. This invention improves the crush-resistant properties of the material from the source by optimizing the alloy composition system, controlling the Mg / Si ratio and modifying with trace amounts of Mn. By using a two-stage homogenization heat treatment combined with a rapid water cooling process, dendrite segregation is fully eliminated and alloy elements are evenly distributed. Rapid cooling also maximizes the retention of supersaturated solid solutions in the matrix, avoiding premature precipitation of the Mg2Si phase and ensuring the uniformity of the microstructure of cast bars from different batches. Combined with a special decompression structure extrusion die, the forming accuracy and microstructure uniformity of the profile are guaranteed, avoiding the risk of crush stress concentration cracking from the forming process.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy material processing technology, specifically to a method for preparing a high-pressure cavitation performance aluminum alloy energy-absorbing box profile for automobiles. Background Technology

[0002] With the rapid development of the automotive industry, vehicle collision safety performance has become one of the core indicators of consumer concern and a key control link in vehicle research and development. The vehicle energy-absorbing box is a core energy-absorbing component installed between the anti-collision steel beam and the longitudinal beam of the vehicle body. When a vehicle collision occurs, the energy-absorbing box absorbs the impact energy of the collision through controllable plastic crumpling deformation. On the one hand, it can minimize the impact of the collision force on the passengers in the vehicle and ensure the safety of the occupants; on the other hand, it can prevent irreversible deformation of core structures such as the longitudinal beam of the vehicle body, thereby reducing the repair costs after a vehicle collision.

[0003] Currently, automotive energy-absorbing boxes are mostly made of 6000 series aluminum alloy profiles through extrusion molding. This series of aluminum alloys has medium strength and good extrusion molding performance, but it still has significant drawbacks in practical applications: The existing aluminum alloy energy-absorbing box has an unreasonable alloy composition system design and improper control of the Mg / Si ratio, which easily leads to the aggregation of free Si to form a hard and brittle phase. At the same time, the iron-rich phase in the matrix is ​​mostly needle-like, which severely cuts the aluminum matrix, resulting in a significant decrease in material toughness. During static crushing tests and actual collisions, the profile is prone to cracks at corners and ribs, making it impossible to achieve stable step-by-step collapse and significantly reducing the energy absorption effect. The homogenization process of cast rods is imperfect. Conventional homogenization processes have problems such as unreasonable holding temperature and insufficient holding time, which cannot effectively eliminate dendrite segregation. Moreover, after homogenization, air cooling or slow cooling is often used, which causes a large amount of Mg2Si strengthening phase dissolved in the aluminum matrix to precipitate prematurely, which greatly reduces the subsequent aging strengthening effect. At the same time, the microstructure and properties of cast rods from different furnaces are inconsistent. The extrusion die design has defects. Conventional diversion dies cannot achieve precise control of the metal flow rate at different positions of the profile. This can easily lead to problems such as insufficient filling at right angle positions and flow rate imbalance at rib positions. At the same time, it can easily cause coarse grain defects in the profile, resulting in large differences in mechanical properties at different positions of the profile. Stress concentration cracking is also likely to occur during the crushing process.

[0004] In summary, existing aluminum alloy energy-absorbing box profile manufacturing technologies cannot simultaneously achieve the desired mechanical properties, crush resistance, and batch stability of the profiles. This makes it difficult to meet the automotive industry's demand for high safety and high consistency in large-scale production of energy-absorbing box components. Therefore, it is urgent to develop a new method for manufacturing aluminum alloy energy-absorbing box profiles to address the aforementioned shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing high-pressure crush-resistant aluminum alloy energy-absorbing box profiles for automobiles. This method can improve the crush-resistant properties of materials from the source by optimizing the alloy composition system, controlling the Mg / Si ratio and modifying with trace amounts of Mn elements. By using a two-stage homogeneous heat treatment combined with a rapid water cooling process, dendrite segregation is fully eliminated and alloy elements are evenly distributed. Furthermore, rapid cooling maximizes the retention of supersaturated solid solutions in the matrix, avoiding premature precipitation of the Mg2Si phase and ensuring the uniformity of the microstructure of cast bars from different batches. Combined with a dedicated decompression structure extrusion die, the forming accuracy and microstructure uniformity of the profile are guaranteed, and the risk of crush stress concentration cracking is avoided from the forming process.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles, the steps of which are as follows: S1. Alloy Composition and Casting: Prepare aluminum alloy smelting raw materials according to the following mass percentages: silicon 0.30-0.50%, magnesium 0.40-0.60%, iron 0.10-0.20%, copper 0-0.10%, manganese 0-0.10%, with the balance being aluminum. Put the raw materials into the smelting furnace for melting. During the smelting process, manganese elements undergo metallurgical bonding with iron elements and excess silicon elements in the aluminum alloy matrix, transforming the harmful needle-like iron-rich phase in the matrix into a skeletal iron-rich manganese phase, reducing the cutting effect of the iron-rich phase on the aluminum matrix. After degassing and slag removal purification treatment of the melt, cast it into round cast rods using a semi-continuous casting process. S2. Two-stage homogenization treatment: The circular casting rod is subjected to two-stage homogenization heat treatment. After the homogenization treatment is completed, the casting rod is taken out of the furnace and rapidly cooled online with high pressure water. After cooling to room temperature of 25°C, it is ready for use. S3. Special extrusion die design: The die adopts an inlet bridge "bowl" type pressure reduction structure, including an upper die and a lower die that are assembled together. The upper die has 9 diversion holes, and the 4 right-angle positions of the profile are directly opposite the diversion holes. The lower die has a welding chamber with a depth of 30mm. S4. Isothermal extrusion molding: The cast rod treated by S2 and the mold of S3 are preheated respectively, and the extrusion cylinder is preheated to 420-450℃ to extrude the energy-absorbing box profile blank. S5. High-strength online water quenching: The energy-absorbing box profile blank is quenched and cooled by a quenching system with uniform water distribution in a 360° circumferential direction for full-coverage cooling, and cooled to room temperature of 25°C. S6. Controlled aging heat treatment: After S5 is quenched and cooled, artificial aging heat treatment is carried out within 6-24 hours to finally obtain the high-pressure crushing performance aluminum alloy energy-absorbing box profile for automobiles.

[0007] Furthermore, the mass ratio of the main alloying element magnesium to silicon (Mg / Si) is 1.2. During the casting process, four or more pre-analyses of the composition are performed to control the mass percentage fluctuation of the main alloying elements magnesium and silicon within the range of ≤0.02%S5. When performing full-coverage cooling, the cooling water pressure is controlled at 600-1000Kpa, the cooling water flow rate at 120-180m³ / h, and the cooling rate at 50-100℃ / s.

[0008] Furthermore, the two-stage homogeneous heat treatment is as follows: In the first stage, the temperature of the homogenizing furnace is raised to 560-580℃ and held for 0.5-2 hours. In the second stage, the temperature of the homogenizing furnace is reduced to 550-570℃ and held for 8-10 hours. The furnace temperature fluctuation range is controlled within ±5℃ throughout the homogeneous heat treatment process.

[0009] Furthermore, in S2, during online rapid cooling, the cooling water pressure is controlled at 600-1000 kPa, the cooling water flow rate at 30-50 m³ / h, and the casting rod cooling rate at 100-300 °C / h.

[0010] Furthermore, the thickness of the flow divider bridge of the upper mold is 24mm, the overall thickness of the upper mold is 115mm, a bowl-shaped countersunk hole with a depth of 10mm is provided at the entrance of the upper mold, the entrance edge of the flow divider bridge is provided with a 20° chamfer, the middle back flow divider hole of the upper mold adopts a two-stage stepped structure, including a first-stage back flow divider hole and a second-stage back flow divider hole arranged coaxially, and the connection between the second-stage back flow divider hole and the perforating cutter adopts a rounded surface transition design; The welding chamber is provided with a beveled surface structure at the edge away from the shaped hole, and a 3.5mm×2° working zone obstruction angle is opened around the entire circumference of the working zone of the shaped hole.

[0011] Furthermore, in S4, the preheating temperature of the casting rod is 460-480℃, the preheating temperature of the die is 460-490℃, and during the extrusion process, isothermal extrusion molding of the profile is achieved by controlling the temperature matching of the casting rod, the die, and the extrusion cylinder.

[0012] Furthermore, in S4, the extrusion ratio is controlled at 45 during the extrusion process, the extrusion discharge speed is 10-13 m / min, the quenching temperature during extrusion is controlled at 550-580℃, and the temperature fluctuation range of each stage in the entire extrusion process is controlled to be ≤±5℃.

[0013] Furthermore, in S5, when performing full-coverage cooling, the cooling water pressure is controlled at 600-1000 kPa, the cooling water flow rate at 120-180 m³ / h, and the cooling rate at 50-100 °C / s.

[0014] Furthermore, in S6, the artificial aging heat treatment includes: The aging furnace is preheated at a target temperature of 175-220℃ for 1 hour. The quenched and cooled energy-absorbing box profile blank is then fed into the preheated aging furnace and held at 175-220℃ for 3-8 hours to complete the aging treatment. During the heating and holding stages of the aging treatment, the furnace temperature fluctuation range is controlled within 20℃.

[0015] Compared with existing technologies, the preparation method of this high-pressure collapsible aluminum alloy energy-absorbing box profile for automobiles has the following advantages: This invention optimizes the alloy composition system and controls the Mg / Si ratio to ensure the full formation of the Mg2Si strengthening phase while avoiding the formation of a hard and brittle phase by free Si, which reduces the material's toughness. At the same time, by adding trace amounts of Mn, the harmful acicular iron-rich phase is transformed into a harmless skeletal iron-manganese-rich phase, reducing the cutting effect on the matrix. This fundamentally improves the alloy's crush resistance. Furthermore, by controlling the fluctuation of the main element composition through multi-frequency pre-analysis, a foundation is laid for consistent performance across product batches.

[0016] This invention employs a two-stage homogeneous heat treatment combined with a rapid water cooling process, which not only fully eliminates dendritic segregation and ensures uniform distribution of alloying elements, but also maximizes the retention of supersaturated solid solutions in the matrix through rapid cooling, preventing premature precipitation of the Mg2Si phase and significantly improving the subsequent aging strengthening effect. At the same time, it ensures the uniformity of the microstructure of cast bars from different heats, thus solving the problems of poor homogenization and coarse precipitates during the cooling process.

[0017] This invention designs a dedicated inlet-type pressure-reducing extrusion die with a bridge-shaped inlet. Through multiple structural designs, including nine flow-diverting holes facing the profile at right angles, a two-stage back flow-diverting hole structure, a beveled welding chamber, and a working zone obstruction angle, it achieves precise control of the metal flow rate at various locations on the profile. This solves the problems of uneven profile filling, flow rate imbalance at ribs, and coarse grain defects, ensuring the profile forming accuracy and microstructure uniformity, and avoiding the risk of stress concentration cracking due to crushing from the forming process perspective.

[0018] This invention achieves full solid solution of the Mg2Si phase and complete recrystallization of the extrusion fiber structure by precisely matching the entire process of extrusion, online quenching, and aging. This eliminates product anisotropy. The high-strength water quenching process avoids grain growth and coarse precipitates, and achieves precise control of the mechanical properties of the profile. This meets the automotive industry's demand for high safety and high consistency in the large-scale production of energy-absorbing box components.

[0019] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0021] Figure 1 A flowchart illustrating the steps of a method for preparing a high-pressure collapsible aluminum alloy energy-absorbing box profile for automobiles; Figure 2 This is a comparison diagram of precipitation under different cooling methods in embodiments of the present invention; Figure 3 This is a schematic diagram of the upper die structure of the special extrusion die in an embodiment of the present invention; Figure 4 This is a schematic diagram of the lower die structure of the special extrusion die in an embodiment of the present invention; Figure 5 This is a model diagram of the ultra-strong quenching system in an embodiment of the present invention; Figure 6 This is a comparison diagram of grain structure under different quenching methods in the embodiments of the present invention; In the diagram: 1. Diverting hole; 2. Primary back diverting hole; 3. Secondary back diverting hole; 4. Lower hole cutter; 5. Through hole; 6. Back hole arc surface; 7. Diverting bridge; 8. Diverting bridge chamfer; 9. Shaped hole; 10. Welding chamber slope; 11. Working zone obstruction angle; 12. Working zone. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0023] To address the limitations of existing aluminum alloy energy-absorbing box profiles, such as susceptibility to cracking and poor energy absorption during static crushing tests, as well as insufficient crushing stability due to large fluctuations in mechanical properties, this invention constructs a method for manufacturing aluminum alloy energy-absorbing box profiles that combines high crushing performance with high mechanical stability through a comprehensive, coordinated design of alloy composition optimization, homogeneous rapid cooling, improved extrusion die structure, high-temperature extrusion recrystallization, high-strength water quenching, and aging processes. Figure 1 As shown, the specific steps of this preparation method are as follows: S1. Prepare aluminum alloy smelting raw materials according to the following mass percentages: silicon 0.30-0.50%, magnesium 0.40-0.60%, iron 0.10-0.20%, copper 0-0.10%, manganese 0-0.10%, with the balance being aluminum. Put the raw materials into a smelting furnace for melting. After degassing and slag removal purification treatment of the melt, cast it into round cast rods using a semi-continuous casting process. S2. Perform two-stage homogenization heat treatment on the round casting rod. After the homogenization treatment is completed, the casting rod is taken out of the furnace and rapidly cooled online with high pressure water. After cooling to 25°C room temperature, it is ready for use. S3. The inlet sinking bridge "bowl" type pressure reduction structure mold is adopted, including the upper mold and the lower mold that are assembled together. The upper mold has 9 diversion holes, and the 4 right-angle positions of the profile are directly opposite the diversion holes. The lower mold has a welding chamber with a depth of 30mm. S4. Preheat the cast rod after S2 treatment and the mold of S3 respectively, and at the same time preheat the extrusion cylinder to 420-450℃ to extrude the energy-absorbing box profile blank. S5. Quenching and cooling the energy-absorbing box profile blank is carried out by a quenching system with 360° uniform water distribution around the circumference for full-coverage cooling, cooling to room temperature of 25°. S6. After S5 is quenched and cooled, artificial aging heat treatment is carried out within 6-24 hours to finally obtain the high-pressure crushing performance aluminum alloy energy-absorbing box profile for automobiles.

[0024] Based on the advantages of lightweight and high strength of aluminum alloy, the crushing morphology and energy absorption effect of the energy-absorbing box are effectively improved. At the same time, by using segmented homogenization and high-strength quenching to control the microstructure to form uniform and fine equiaxed grains, a complete aluminum alloy energy-absorbing box production solution is formed, which has high process stability, good product consistency, excellent crushing performance, and no risk of crushing cracking.

[0025] This invention is primarily applied to the industrial-scale production of energy-absorbing structural components in fields such as automobile manufacturing and rail transportation. Traditional processes suffer from large fluctuations in alloy composition, insufficient homogeneous cooling, unreasonable mold design, and inadequate quenching strength, resulting in uneven internal structure and prominent coarse-grain defects in the profiles. During crushing, corner cracking or cracking of the central ribs easily occurs, making it difficult to meet safety standards for energy absorption. Existing improved processes also suffer from problems such as large fluctuations in mechanical properties between different furnace batches and low crushing yield. This invention achieves stable control of energy-absorbing box profiles through precise control of the Mg / Si ratio, homogeneous rapid cooling to preserve supersaturated solid solution, inlet undercut bowl mold design, high-temperature extrusion recrystallization to eliminate anisotropy, and high-strength water quenching to obtain uniform equiaxed grains. This makes it suitable for automotive safety applications and continuous industrial production.

[0026] Performance Testing Specifications For the aluminum alloy energy-absorbing box profiles prepared in Embodiment 1 and the comparative example of the present invention, all performance tests were completed using the same standards, equipment, and environment. The test environment was room temperature (23±5℃) and humidity maintained at 45%-65%. All samples were conditioned under the same conditions for 24 hours before testing to ensure the comparability, objectivity, and accuracy of the test results. Mechanical property testing: Tensile tests were conducted using an electronic universal testing machine to determine the tensile strength, yield strength, and elongation after fracture of the samples. Five valid specimens were tested for each group of samples, and the arithmetic mean was taken as the final result.

[0027] Static crushing performance test: An axial static compression test is performed on a universal press with a compression stroke set to 200 mm. The load is continuously applied until the specified stroke is completed. The energy absorbed is recorded and calculated. The crushing yield (the percentage of samples with a crushing grade of 1 out of the total number of test samples) is statistically analyzed. The surface of the sample after crushing is visually inspected for cracks.

[0028] Batch stability test: 10 independent batches of profiles were produced continuously. 10 samples were randomly selected from each batch to test the yield strength. The maximum fluctuation value of yield strength between any batch and the maximum fluctuation value of yield strength within the same production batch were statistically analyzed and calculated. Example 1

[0029] This embodiment employs a complete process route including optimal component ratio, two-stage homogenization, rapid water cooling, bowl-type decompression die, precision extrusion, high-strength online water quenching, and medium-temperature aging. Alloy elements are controlled at intermediate values, with Mg / Si precisely at 1.2. The aim is to verify the optimal implementation effect of the core technical solution of this invention, focusing on verifying whether the mechanical properties, crush resistance, energy absorption, and batch stability of the profiles meet the design specifications.

[0030] This embodiment provides a method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles. The specific steps are as follows: S1. Alloy Composition and Casting: The alloy raw materials are prepared according to the following mass percentages: silicon 0.40%, magnesium 0.48%, iron 0.15%, copper 0.05%, manganese 0.08%, with the balance being aluminum; wherein Mg / Si=1.2. The prepared raw materials are added to the melting furnace and melted. After the melt is purified by degassing and slag removal, it is cast into Φ200mm ingots using a semi-continuous casting process. Four pre-analysis of the composition is performed during the casting process to control the mass percentage fluctuation range of magnesium and silicon elements to ≤0.02%.

[0031] S2. Homogenization Treatment: The cast ingot undergoes a two-stage homogenization heat treatment. In the first stage, the furnace temperature is rapidly raised to 570℃ and held for 1 hour. In the second stage, the furnace temperature is lowered to 560℃ and held for 9 hours. The temperature fluctuation range is controlled within ±5℃ throughout the homogenization process. After homogenization, the cast ingot is removed from the furnace and immediately subjected to rapid cooling with strong water. The cooling water pressure is controlled at 800 kPa, the cooling water flow rate at 40 m³ / h, and the cooling rate at 200℃ / h, until the ingot is cooled to room temperature. The rapid cooling process with strong water used in this embodiment can effectively suppress the premature precipitation of the Mg2Si strengthening phase during the cooling process of the cast ingot. Its microstructure is similar to that of conventional air cooling processes. Figure 2 As shown: Figure 2 (A) is the precipitated phase structure after rapid cooling. The number of precipitates at the grain boundaries is very small and the size is small. A large amount of supersaturated solid solution is retained in the matrix. Figure 2 (B) shows the precipitate structure after conventional cooling. A large number of coarse precipitates appear at the grain boundaries, which severely rupture the aluminum matrix, verifying the significant advantage of rapid cooling in this invention.

[0032] S3. Extrusion Die Design and Fabrication: The extrusion die adopts an inlet sunken bridge "bowl" type pressure reduction structure, including a matching upper die and lower die; the upper die structure is as follows: Figure 3 As shown, the upper die has 9 diversion holes 1, and the profile has 4 right-angle positions directly opposite each diversion hole 1; the thickness of the diversion bridge 7 of the upper die is 24mm, the overall thickness of the upper die is 115mm, and the depth of the inlet "bowl" countersunk hole is 10mm; the inlet edge of the diversion bridge 7 is chamfered at 20°; the middle back diversion hole of the upper die adopts a two-stage stepped structure, including a first-stage back diversion hole and a second-stage back diversion hole arranged coaxially, and the connection between the second-stage back diversion hole and the piercing cutter adopts a back hole arc surface transition design; the lower die structure is as follows. Figure 4 As shown, the lower mold has a welding chamber with a depth of 30mm. The welding chamber is set with a welded chamber slope at the edge away from the hole. The working zone of the hole has a 3.5mm×2° obstruction angle around the entire circumference. During the mold preparation process, the flow holes of the upper mold and the lower hole cutter of the mold head are precision milled, and the surface roughness Ra=0.6μm after processing. The through holes of the middle rib are processed by wire cutting with wire cutting process.

[0033] S4. Extrusion: Preheat the cast rod processed in step S2 to 470℃, preheat the extrusion die prepared in step S3 to 480℃, and preheat the extrusion cylinder to 435℃; control the extrusion ratio to 45, the extrusion discharge speed to 12m / min, control the extrusion quenching temperature to 565℃, and control the temperature fluctuation range to ≤±5℃ throughout the extrusion process to extrude the energy-absorbing box profile of the target specifications.

[0034] S5 Quenching: The profile extruded in step S4 is quenched and cooled online using a high-strength water quenching process, employing methods such as... Figure 5The ultra-strong quenching system with uniform 360° circumferential water distribution shown features multiple sets of annular water spray rings along the profile extrusion direction. Each set of spray rings has multiple high-pressure nozzles evenly arranged circumferentially on its inner side. All nozzles spray towards the central axis of the profile, ensuring uniform cooling intensity across the profile's circumference. The cooling water pressure is controlled at 800 kPa, the cooling water flow rate at 150 m³ / h, and the profile cooling rate at 75°C / s, cooling to room temperature. The ultra-strong quenching process used in this embodiment effectively inhibits alloy grain growth. Its grain structure is compared with that of conventional quenching processes. Figure 6 As shown: Figure 6 (A) is the grain structure under ultra-strong quenching conditions. The grain size is small and uniform, which is a typical equiaxed grain structure. Figure 6 (B) shows the grain structure under conventional quenching conditions. The grains are coarse and uneven in size, with obvious grain growth, which verifies the significant effect of the high-strength water quenching process of the present invention on the microstructure refinement.

[0035] S6 Aging: The profile quenched in step S5 is subjected to aging heat treatment within 12 hours; the aging furnace is preheated at 190℃ for 1 hour, and then the profile is sent into the aging furnace and held at 190℃ for 5 hours to complete the aging treatment and obtain aluminum alloy energy-absorbing box profile; the temperature fluctuation range during the heating and holding stages of the aging treatment is controlled within 15℃.

[0036] The profile obtained in this embodiment has a tensile strength of 245 MPa, a yield strength of 212 MPa, an elongation of 12.5%, and absorbs 24.6 KJ of energy at a compression stroke of 200 mm in the static crushing test. The crushing yield is 99.2%, and there are no cracks on the surface after crushing. The maximum fluctuation of yield strength between batches is 8 MPa, and the maximum fluctuation of yield strength within the same batch is 4 MPa. This verifies that the optimal process parameters of this invention can achieve the comprehensive performance of high crushing, high toughness, and high stability of the energy-absorbing box profile. Example 2

[0037] This embodiment employs a combination of lower limits for composition, homogenization process, extrusion parameters, quenching parameters, and long-term low-temperature aging to simulate a conservative process setting in production. This verifies that the technical solution of this invention can still meet the minimum requirements for mechanical properties and crush resistance of automotive energy-absorbing box profiles within the lower limit parameter range, thus confirming the feasibility of the lower limit of the process window.

[0038] This embodiment provides a method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles. The specific steps are as follows: S1. Alloy Composition and Casting: The alloy raw materials are prepared according to the following mass percentages: silicon 0.30%, magnesium 0.36%, iron 0.10%, copper 0.02%, manganese 0.05%, with the balance being aluminum and unavoidable impurities; wherein Mg / Si=1.2. The prepared raw materials are added to the melting furnace for melting. After the melt is purified by degassing and slag removal, it is cast into Φ200mm ingots using a semi-continuous casting process. Five pre-analyses of the composition are performed during the casting process to control the mass percentage fluctuation range of magnesium and silicon to ≤0.02%.

[0039] S2. Homogenization treatment: The cast rod undergoes a two-stage homogenization heat treatment. In the first stage, the furnace temperature is rapidly raised to 560℃ and held for 2 hours. In the second stage, the furnace temperature is lowered to 550℃ and held for 10 hours. The temperature fluctuation range is controlled within ±5℃ throughout the homogenization treatment. After homogenization, the cast rod is removed from the furnace and immediately cooled rapidly with strong water. The cooling water pressure is controlled at 600Kpa, the cooling water flow rate is 30m³ / hour, and the casting rod cooling rate is 100℃ / hour, until it is cooled to room temperature.

[0040] S3. Extrusion die design and preparation: completely consistent with Example 1.

[0041] S4. Extrusion: Preheat the cast rod processed in step S2 to 460℃, preheat the extrusion die prepared in step S3 to 460℃, and preheat the extrusion cylinder to 420℃; control the extrusion ratio to 45, the extrusion discharge speed to 10m / min, control the extrusion quenching temperature to 550℃, and control the temperature fluctuation range to ≤±5℃ throughout the extrusion process to extrude the energy-absorbing box profile of the target specifications.

[0042] S5. Quenching: The profiles extruded in step S4 are quenched online using a high-strength water quenching process. A quenching system with uniform circumferential water distribution is used, with the cooling water pressure controlled at 600 kPa, the cooling water flow rate at 120 m³ / h, and the profile cooling rate at 50 ℃ / s, until the profiles are cooled to room temperature.

[0043] S6. Aging: The profile quenched in step S5 is subjected to aging heat treatment within 24 hours. First, the aging furnace is preheated at 175℃ for 1 hour, and then the profile is sent into the aging furnace and held at 175℃ for 8 hours to complete the aging treatment and obtain aluminum alloy energy-absorbing box profile. During the heating and holding stages of the aging treatment, the temperature fluctuation range is controlled within 20℃.

[0044] The profile prepared in this embodiment has a tensile strength of 228 MPa, a yield strength of 203 MPa, an elongation of 11.2%, and absorbs 22.1 KJ of energy at a compression stroke of 200 mm in the static crush test. The crushing yield is 98.5%, and there are no cracks on the surface after crushing. The maximum fluctuation of yield strength between batches is 12 MPa, and the maximum fluctuation of yield strength within the same batch is 6 MPa, proving that the lower limit parameters of the process of this invention can still stably prepare qualified high-pressure crushing energy-absorbing box profiles. Example 3

[0045] This embodiment uses a combination of upper limits for composition, homogenization process, extrusion parameters, quenching parameters, and short-term high-temperature aging to verify whether the profile performance is still controllable within the upper limit parameter range and whether defects such as overheating, cracking, and coarse grains occur, thus confirming the feasibility of the upper limit of the process window.

[0046] This embodiment provides a method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles. The specific steps are as follows: S1. Alloy Composition and Casting: The alloy raw materials are prepared according to the following mass percentages: silicon 0.50%, magnesium 0.60%, iron 0.20%, copper 0.10%, manganese 0.10%, with the balance being aluminum and unavoidable impurities; wherein Mg / Si=1.2. The prepared raw materials are added to the melting furnace for melting. After the melt is purified by degassing and slag removal, it is cast into Φ200mm ingots using a semi-continuous casting process. Six pre-composition analyses are performed during the casting process to control the mass percentage fluctuation range of magnesium and silicon elements to ≤0.02%.

[0047] S2. Homogenization treatment: The cast rod undergoes a two-stage homogenization heat treatment. In the first stage, the furnace temperature is rapidly raised to 580℃ and held for 0.5 hours. In the second stage, the furnace temperature is lowered to 570℃ and held for 8 hours. The temperature fluctuation range is controlled within ±5℃ throughout the homogenization treatment. After homogenization, the cast rod is removed from the furnace and immediately cooled rapidly with strong water. The cooling water pressure is controlled at 1000Kpa, the cooling water flow rate is 50m³ / hour, and the casting rod cooling rate is 300℃ / hour, until it reaches room temperature.

[0048] S3. Extrusion die design and preparation: completely consistent with Example 1.

[0049] S4. Extrusion: Preheat the cast rod processed in step S2 to 480℃, preheat the extrusion die prepared in step S3 to 490℃, and preheat the extrusion cylinder to 450℃; control the extrusion ratio to 45, the extrusion discharge speed to 13m / min, control the extrusion quenching temperature to 580℃, and control the temperature fluctuation range to ≤±5℃ throughout the extrusion process to extrude the energy-absorbing box profile of the target specifications.

[0050] S5. Quenching: The profiles extruded in step S4 are quenched online using a high-strength water quenching process. A quenching system with uniform circumferential water distribution is used, with the cooling water pressure controlled at 1000 kPa, the cooling water flow rate at 180 m³ / h, and the profile cooling rate at 100 ℃ / s, until the profiles are cooled to room temperature.

[0051] S6. Aging: The profile quenched in step S5 is subjected to aging heat treatment within 6 hours; the aging furnace is preheated at 220℃ for 1 hour, and then the profile is sent into the aging furnace and held at 220℃ for 3 hours to complete the aging treatment and obtain aluminum alloy energy-absorbing box profile; the temperature fluctuation range during the heating and holding stages of the aging treatment is controlled within 20℃.

[0052] The profiles obtained in this embodiment have a tensile strength of 258 MPa, a yield strength of 236 MPa, an elongation of 9.8%, and absorb 21.8 KJ of energy at a compression stroke of 200 mm in the static crush test. The crushing yield is 98.2%, and there are no cracks on the surface after crushing. The maximum fluctuation of yield strength between batches is 15 MPa, and the maximum fluctuation of yield strength within the same batch is 8 MPa. This proves that the upper limit parameters of the process of this invention will not lead to performance degradation or defects, and that the process window is wide and the production error tolerance is high.

[0053] Comparative Example 1 This comparative example uses conventional processes such as existing 6061 aluminum alloy composition, single-stage homogeneous air cooling, ordinary diversion die, conventional extrusion, low-speed quenching, and delayed aging as a blank control to highlight the progress of this invention compared to the prior art.

[0054] This comparative example uses the existing conventional method for preparing 6061 aluminum alloy energy-absorbing box profiles. The specific steps are as follows: S1. Alloy composition and casting: The conventional 6061 aluminum alloy composition is used, with silicon 0.40-0.8%, magnesium 0.8-1.2%, and the balance being aluminum. It is cast into a Φ200mm ingot. Only one composition analysis is performed during the casting process.

[0055] S2. Homogenization: The conventional single-stage homogenization process is adopted, and the temperature is kept at 560℃ for 8 hours. After being taken out of the furnace, it is air-cooled to room temperature.

[0056] S3. Extrusion Die: It adopts a conventional planar flow divider die. The upper die is equipped with 6 flow divider holes and has no secondary back flow divider hole structure. The lower die welding chamber has no inclined surface design and the working zone has no obstruction angle design.

[0057] S4. Extrusion: Preheating temperature of casting rod 450℃, preheating temperature of die 450℃, extrusion cylinder temperature 410℃, extrusion discharge speed 8m / min, extrusion quenching temperature 520℃.

[0058] S5. Quenching: The conventional air cooling + water mist cooling process is adopted, and the cooling rate is ≤20℃ / s.

[0059] S6. Aging: After extrusion, the profiles are placed for 72 hours and then aged, and kept at 170℃ for 6 hours.

[0060] The conventional profiles prepared in this comparative example have a tensile strength of 260 MPa, a yield strength of 245 MPa, and an elongation of only 6.5%. In the static crush test, the energy absorbed at a compression stroke of 200 mm is only 15.3 KJ, and the crushing yield is only 62.5%. After crushing, obvious cracks appear at the corners and ribs. The maximum fluctuation in yield strength between batches is 38 MPa, and the maximum fluctuation in yield strength within the same batch is 22 MPa. The performance is extremely poor and the batches are extremely unstable, which completely fails to meet the requirements for use in automotive high-pressure crushing energy absorption boxes.

[0061] Comparative Example 2 This comparative example only changed the Mg / Si ratio to 0.8, while all other process parameters were completely consistent with those in Example 1. It was used to verify the key influence of the Mg / Si ratio on the toughness and crush resistance of the material.

[0062] The only difference between this comparative example and Example 1 is that in step S1, the alloy composition is 0.60% silicon, 0.48% magnesium, and Mg / Si = 0.8. All other steps and parameters are the same as in Example 1.

[0063] The profiles prepared in this comparative example have a tensile strength of 232 MPa, a yield strength of 208 MPa, and an elongation of only 7.2%. In the static crush test, the energy absorbed at a compression stroke of 200 mm is 17.5 KJ, and the crushing yield is 76.3%. Local microcracks appear after crushing. The maximum fluctuation in yield strength between batches is 16 MPa, and the maximum fluctuation in yield strength within the same batch is 9 MPa. Due to the improper Mg / Si ratio, free Si is generated into a hard and brittle phase, which significantly deteriorates the toughness and crushing performance.

[0064] Comparative Example 3 This comparative example only changes the cooling method after homogenization, using air cooling instead of the rapid water cooling of the present invention. All other process parameters are completely consistent with those of Example 1. It is used to separately verify the key role of rapid cooling after homogenization in solid solution effect and tissue uniformity.

[0065] The only difference between this comparative example and Example 1 is that in step S2, after homogenization, air cooling is used for cooling, with a cooling rate ≤50℃ / hour. The remaining steps and parameters are the same as in Example 1.

[0066] The profiles prepared in this comparative example have a tensile strength of 215 MPa, a yield strength of 192 MPa, an elongation of 10.5%, and an energy absorption of 18.2 KJ when the compression stroke is 200 mm in the static crush test. The crushing yield is 81.4%, and microcracks appear at the corners after crushing. The maximum fluctuation in yield strength between batches is 24 MPa, and the maximum fluctuation in yield strength within the same batch is 15 MPa. The slow cooling caused premature precipitation of Mg2Si, resulting in insufficient strength and poor batch stability.

[0067] Comparative Example 4 This comparative example only reduces the extrusion quenching temperature to 520℃, which is lower than the 550-580℃ range of this invention. All other process parameters are completely consistent with those of Example 1. This example is used to verify the key effects of extrusion quenching temperature on recrystallization and anisotropy.

[0068] The only difference between this comparative example and Example 1 is that in step S4, the extrusion quenching temperature is controlled at 520℃, while the other steps and parameters are the same as in Example 1.

[0069] The profiles prepared in this comparative example have a tensile strength of 218 MPa, a yield strength of 195 MPa, an elongation of 9.2%, and absorb 18.6 KJ of energy at a compression stroke of 200 mm in the static crush test. The crushing yield rate is 83.5%, and microcracks appear in the ribs after crushing. The maximum fluctuation in yield strength between batches is 21 MPa, and the maximum fluctuation in yield strength within the same batch is 12 MPa. The crushing cracks are caused by insufficient solid solution due to insufficient quenching temperature, failure to eliminate fiber structure, and anisotropy.

[0070] Comparative Example 5 This comparative example only reduces the quenching cooling rate, using conventional water mist with a cooling rate of 20℃ / s, which is lower than the 50-100℃ / s of this invention. All other process parameters are completely consistent with Example 1. It is used to independently verify the key role of high-strength online quenching in grain uniformity and crack resistance.

[0071] The only difference between this comparative example and Example 1 is that in step S5, a conventional water mist quenching process is used with a cooling rate of 20°C / s. All other steps and parameters are the same as in Example 1.

[0072] The profiles prepared in this comparative example have a tensile strength of 222 MPa, a yield strength of 205 MPa, and an elongation of only 7.8%. In the static crush test, the energy absorbed at a compression stroke of 200 mm is 19.1 KJ, and the crushing yield is 85.2%. Local microcracks appear after crushing. The maximum fluctuation in yield strength between batches is 18 MPa, and the maximum fluctuation in yield strength within the same batch is 10 MPa. Insufficient cooling rate leads to coarse grains, uneven microstructure, and decreased toughness and crushing resistance.

[0073] To fully verify the technical effectiveness of the preparation method of this invention, mechanical properties, static crushing performance, and batch stability tests were conducted on the aluminum alloy energy-absorbing box profiles prepared in the embodiments and comparative examples of this invention, in accordance with the standards of the unified performance testing instructions. The test results are summarized in the table below: .

[0074] As shown in the table above, the aluminum alloy energy-absorbing box profiles prepared in the embodiments of the present invention are superior to the comparative samples in all performance indicators. Among them, Example 1, as the optimal combination of process parameters, produces a profile with a tensile strength of 245 MPa, a yield strength of 212 MPa, an elongation of 12.5%, and a static crushing energy absorption of up to 24.6 KJ over a 200 mm stroke. The crushing yield is 99.2%, and there are no cracks on the surface after crushing. The maximum fluctuation in yield strength between batches is only 8 MPa, and the maximum fluctuation within the same batch is only 4 MPa. All indicators significantly exceed the design requirements. Examples 2 and 3 respectively verify the feasibility of the lower and upper limits of the process parameters, proving that the present invention has a wide process window and a high production tolerance. Comparative Example 1, using existing conventional processes, had an elongation of only 6.5%, energy absorption of only 15.3 KJ, and a crushing yield of only 62.5%. It exhibited obvious cracking after crushing, and the batch performance fluctuated greatly, completely failing to meet the usage requirements. Comparative Examples 2-5 deviated from the core technical features of this invention, such as the Mg / Si ratio, homogeneous cooling method, extrusion quenching temperature, and quenching cooling rate. They all showed problems such as decreased elongation, reduced crushing grade, insufficient yield, and deteriorated batch stability, fully demonstrating the necessity of synergistic optimization of alloy composition, mold structure, and the entire process of this invention.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles, characterized in that, The preparation method involves the following steps: S1. Alloy Composition and Casting: Prepare aluminum alloy smelting raw materials according to the following mass percentages: silicon 0.30-0.50%, magnesium 0.40-0.60%, iron 0.10-0.20%, copper 0-0.10%, manganese 0-0.10%, with the balance being aluminum. Put the raw materials into the smelting furnace for melting. After degassing and slag removal purification treatment of the melt, cast it into round ingots using a semi-continuous casting process. S2. Two-stage homogenization treatment: The circular casting rod is subjected to two-stage homogenization heat treatment. After the homogenization treatment is completed, the casting rod is taken out of the furnace and rapidly cooled online with high pressure water. After cooling to room temperature of 25°C, it is ready for use. S3. Special extrusion die design: A special extrusion die is adopted, including an upper die and a lower die that are assembled together. The upper die has 9 diversion holes, and the four right-angle positions of the profile are directly opposite the diversion holes. The lower die has a welding chamber with a depth of 30mm. S4. Isothermal extrusion molding: The cast rod treated by S2 and the special extrusion die of S3 are preheated respectively, and the extrusion cylinder is preheated to 420-450℃ to extrude the energy-absorbing box profile blank. S5. High-strength online water quenching: The energy-absorbing box profile blank is quenched and cooled by a quenching system with uniform water distribution in a 360° circumferential direction for full-coverage cooling, and cooled to room temperature of 25°C. S6. Controlled aging heat treatment: After S5 is quenched and cooled, artificial aging heat treatment is carried out within 6-24 hours to finally obtain the high-pressure crushing performance aluminum alloy energy-absorbing box profile for automobiles.

2. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, The mass ratio of the main alloying element magnesium to silicon, Mg / Si, is 1.2, and the composition is pre-analyzed four or more times during the casting process.

3. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, The two-stage homogeneous heat treatment is as follows: In the first stage, the temperature of the homogenizing furnace is raised to 560-580℃ and held for 0.5-2 hours. In the second stage, the temperature of the homogenizing furnace is reduced to 550-570℃ and held for 8-10 hours.

4. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, In S2, during online rapid cooling, the cooling water pressure is controlled at 600-1000 kPa, the cooling water flow rate at 30-50 m³ / h, and the casting rod cooling rate at 100-300 °C / h.

5. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, The thickness of the flow divider bridge of the upper mold is 24mm, the overall thickness of the upper mold is 115mm, a bowl-shaped countersunk hole with a depth of 10mm is provided at the entrance of the upper mold, the entrance edge of the flow divider bridge is provided with a 20° chamfer, the middle back flow divider hole of the upper mold adopts a two-stage stepped structure, including a first-stage back flow divider hole and a second-stage back flow divider hole arranged coaxially, and the connection between the second-stage back flow divider hole and the perforating cutter adopts a rounded surface transition design; The welding chamber is provided with a beveled surface structure at the edge away from the shaped hole, and a 3.5mm×2° working zone obstruction angle is opened around the entire circumference of the working zone of the shaped hole.

6. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, In step S4, the preheating temperature of the casting rod is 460-480℃, and the preheating temperature of the mold is 460-490℃.

7. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, In S4, the extrusion ratio is controlled at 45 during the extrusion process, the extrusion discharge speed is 10-13 m / min, and the quenching temperature during extrusion is controlled at 550-580℃.

8. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, In S5, when performing full-coverage cooling, the cooling water pressure is controlled at 600-1000 kPa, the cooling water flow rate is 120-180 m³ / h, and the cooling rate is 50-100 °C / s.

9. The method for preparing a high-pressure collapsibility aluminum alloy energy-absorbing box profile for automobiles according to claim 1, characterized in that, In step S6, the artificial aging heat treatment includes: Preheat the aging furnace at a target temperature of 175-220℃ for 1 hour, then send the quenched and cooled energy-absorbing box profile blank into the preheated aging furnace and hold it at 175-220℃ for 3-8 hours to complete the aging treatment.

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